Disclosure of Invention
The present invention is directed to solving the above-mentioned problems, and an object of the present invention is to provide a gallium nitride sensor, a method of manufacturing the same, and a multi-sensor system, which are capable of better detecting the concentration of an analyte in contact with a sensing region by a functional process of the sensing region of a Transistor having a group III nitride based HEMT (High Electron Mobility Transistor) structure.
The invention further solves the problems of improving the detection effect and reducing the detection difficulty by optimizing the sensing area.
One aspect of the present invention provides a gallium nitride sensor, comprising: a hetero-semiconductor substrate, and a group III nitride based HEMT structure transistor thereon; the source electrode and drain electrode metal of the transistor are arranged on the semiconductor on the top layer of the transistor, the surface of the grid electrode is provided with a functionalized film obtained through functionalization treatment, and a sensing area is formed in a grid electrode area exposed between the source electrode and the drain electrode; optimizing the sensing area by performing recess etching or thinning the sensing layer on the sensing area; and using the sensing area after the optimization processing to detect the concentration of the object to be detected, which is in contact with the sensing area, by detecting the current change of the sensing area.
Wherein, the transistor includes: at least one group III nitride heterojunction is contained, one side of the group III nitride heterojunction is GaN, and the other side is other binary or ternary group III nitride.
Wherein the group III nitride heterojunction comprises: the buffer layer is positioned on the heterogeneous semiconductor substrate, is used as a current channel and comprises GaN; and a barrier layer on the buffer layer, the barrier layer having a composition comprising a multi-element group III nitride or ZnO and/or an intrinsic material; the components of the buffer layer and the barrier layer interact with each other to form two-dimensional electron gas at the interface of the buffer layer and the barrier layer; ohmic contact source electrode and drain electrode metal are positioned on the barrier layer, the barrier layer exposed between the ohmic contact source electrode and the drain electrode metal is a sensing area, and the functionalized film is coated on the sensing area; and the insulating layer is wrapped on the peripheries of the ohmic contact source electrode metal, the ohmic contact drain electrode metal, the two-dimensional electron gas and the barrier layer and is embedded into one side of the buffer layer, which is close to the barrier layer.
Preferably, the group III nitride heterojunction, further comprises: a capping layer overlying the barrier layer, the capping layer having a composition that is doped or interacts with the barrier layer using intrinsic materials to form ohmic contacts to source and drain metals on the capping layer; the exposed covering layer between the ohmic contact source electrode and the ohmic contact drain electrode metal is a sensing area; and the insulating layer is also coated on the periphery of the covering layer. Wherein the thickness of the covering layer is 1-3 microns.
Wherein, the multi-element III group nitride in the barrier layer comprises any one of GaN, InN, AlN, AlGaN, InGaN and AlInGaN; when AlGaN is adopted, the thickness of the barrier layer is 15-35 nm, and the molar ratio of Al element is 15-35%; when AlN is adopted, the thickness of the barrier layer is 2-8 nanometers; and/or the insulating layer comprises any one of insulating metal, insulating oxide and high molecular polymer.
Specifically, the hetero semiconductor substrate includes: growing group III nitride on a corresponding extrinsic semiconductor substrate in an epitaxial manner, wherein the extrinsic semiconductor comprises any one of silicon, silicon carbide, sapphire and aluminum nitride; and/or the functionalized membrane comprises any one or more of oxide, metal thin film, nano material, semiconductor, nitride, organic biological material, inorganic material and high molecular material.
In accordance with the above sensor, another aspect of the present invention provides a multi-sensor system, comprising: at least two sensors and a main control circuit; the at least two sensors are connected between the main control circuit and the object to be detected in parallel; and the output signal of the sensor is controlled and analyzed through the main control circuit, so that the concentration detection of the object to be detected is realized.
In another aspect, the present invention provides a method for preparing the above gallium nitride sensor, including: forming a separated mesa structure on the heterogeneous semiconductor substrate by adopting a plasma etching method; wherein the hetero semiconductor substrate includes: growing group III nitride epitaxially on the corresponding extrinsic semiconductor substrate; based on the mesa structure, sequentially performing surface oxide removal treatment, metal precipitation and patterning treatment and high-temperature annealing treatment to form ohmic contact source and drain metal on the top of the mesa structure; based on a mesa structure with ohmic contact source electrode and drain electrode metal formed on the top, ohmic contact insulation and metal deposition intercommunication contact processing and interconnection metal deposition and forming processing are sequentially carried out, and a sensing area is formed between the ohmic contact source electrode and the drain electrode metal on the top of the mesa structure; performing functionalization treatment on the sensing area formed by the treatment, and forming a functionalized film on the sensing area; and carrying out metal interconnection insulation or packaging treatment on the mesa structure which is formed based on the ohmic contact source electrode and drain electrode metal and the functionalized film to obtain the sensor.
Preferably, the method further comprises the following steps: when the sensor adopts AlGaN as a barrier layer, groove etching treatment is carried out on a sensing area formed by the treatment so as to reduce the thickness of the sensing area to a value required by detection.
According to the scheme of the invention, the exposed grid region between the source electrode and the drain electrode of the transistor with the III-nitride-based HEMT structure which is very similar to the structure of the HEMT is functionalized (for example, a functionalized film is coated on the surface of the grid electrode of the transistor with the GaN-based HEMT structure), when the grid region is contacted with the detected analyte, the current between the source electrode and the drain electrode can be obviously changed, and then the purpose of detecting the concentration of the analyte is realized by detecting the change of the current.
Furthermore, according to the scheme of the invention, the sensing area is optimized by means of recess etching of the sensing area or thinning of the sensing layer, so that the response time, the detection range and the sensitivity of the sensor can be improved.
Therefore, the scheme of the invention solves the problems of processing the transistor sensing region of the III-nitride-based HEMT structure, better realizing the concentration detection of the analyte contacting with the sensing region, improving the detection effect and reducing the detection difficulty, thereby overcoming the defects of low sensitivity, small detection range and poor portability in the prior art and realizing the beneficial effects of high sensitivity, large detection range and good portability.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.
The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be clearly and completely described below with reference to the specific embodiments of the present invention and the accompanying drawings. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
According to an embodiment of the present invention, a gallium nitride sensor is provided, as shown in fig. 1, which is a schematic cross-sectional structure diagram of an embodiment of the gallium nitride sensor of the present invention. The sensor at least comprises:
a hetero-semiconductor substrate, and a group III nitride (e.g., gallium nitride) -based HEMT structure transistor located thereon; the source electrode and drain electrode metal of the transistor are arranged on the semiconductor on the top layer of the transistor, the surface of the grid electrode is provided with a functionalized film 11 obtained through functionalization treatment, and a sensing area is formed in a grid electrode area exposed between the source electrode and the drain electrode; and the concentration detection of the object to be detected which is contacted with the sensing area is realized by detecting the current change of the sensing area. By adopting the transistor with the GaN-based HEMT structure, the size of the sensor can be reduced, and the detection sensitivity of the sensor can be improved.
In one example, the outer surface of the transistor is a semiconductor material layer, the source and drain metals (e.g., ohmic contact source and drain metals 7) of the transistor both extend out of the semiconductor material layer (e.g., are disposed on the top semiconductor material layer), the gate is exposed between the source and drain, the gate region between the source and drain is the sensing region 10, and the gate surface is functionalized to have the functionalized film 11. The current between the source and drain is then conducted through a two-dimensional electron gas resulting from the polarization effect created by the stack of two different group III nitrides. The sensing function is realized by a naked grid between a source electrode and a drain electrode, and when the grid region is contacted with an analyte to be detected, the current between the source electrode and the drain electrode is obviously changed.
Wherein, heterogeneous semiconductor substrate includes: group III nitride is epitaxially grown on a corresponding extrinsic semiconductor substrate 2, the extrinsic semiconductor comprising any one of silicon, silicon carbide, sapphire, aluminum nitride, and the like. The epitaxial growth needs to be applied to MBE (Molecular Beam Epitaxy, which is a new crystal growth technique) or MOCVD (Metal-organic Chemical Vapor Deposition) technique.
The functionalized film 11 includes any one or more of an oxide, a metal thin film, a nano material, a semiconductor, a nitride, an organic biological material, an inorganic material and a high molecular material.
For example: the functionalized membrane 11: the sensor must be capable of detecting the target analyte, at least sensitive to contaminants that are often present in the substance being measured. The selectivity for a particular analyte is achieved by a functionalized coating (e.g., functionalized membrane 11) on the sensing region 10 that is only active for a particular analyte and not active for other substances. The functionalized materials referred to herein include, but are not limited to, intrinsic or extrinsic oxides (metal or nonmetal oxides), thin metal films (e.g., Pt, Au, Ag), nanomaterials [ e.g.: CNTs (Carbon nanotubes), graphene, ZnO nanorods, etc.), as well as nanoparticles, semiconductors (e.g., InN), nitrides (e.g., SiN, TiN), organic biomaterials (e.g., ionophores), inorganic materials, polymeric materials, and combinations thereof.
In one embodiment, a transistor includes: containing at least one group III nitride heterojunction with GaN on one side (e.g., the side away from the transistor surface) and other binary [ e.g.: (aluminum nitride (AlN), indium nitride (InN)) or ternary [ e.g., aluminum gallium nitride (AlGaN), indium gallium nitride (InGaN) ] group III nitrides.
In one embodiment, a group III nitride heterojunction, comprises: a buffer layer 3 on the hetero semiconductor substrate for reducing stress, reducing defect density, and electrically insulating, the buffer layer 3 serving as a current path and having a composition of GaN; and a barrier layer 5 on the buffer layer 3, the barrier layer 5 having a composition comprising a multi-element group III nitride or ZnO and/or an intrinsic material; the components of the buffer layer 3 and the barrier layer 5 interact with each other, and two-dimensional electron gas 4 is formed at the interface of the buffer layer 3 and the barrier layer 5; ohmic contact source electrode and drain electrode metal 7 are positioned on the barrier layer 5, the barrier layer exposed between the ohmic contact source electrode and the drain electrode metal 7 is a sensing area 10, and the functionalized film 11 is coated on the sensing area 10; and the insulating layer 8 is coated on the peripheries of the ohmic contact source electrode and drain electrode metal 7, the two-dimensional electron gas 4 and the barrier layer 5 and is embedded into one side of the buffer layer 3 close to the barrier layer 5.
Wherein the insulating layer 8 at the same time encloses the edge 9 for a better insulating effect.
In one example, the buffer layer 3 may be constructed using techniques known to those skilled in the art. For example, the material of the buffer layer 3 may be doped or intrinsic non-doped as needed.
The 2DEG refers to a phenomenon in which an electron gas can freely move in two dimensions and is restricted in a third dimension, which is the basis of the operation of many field effect devices (e.g., MOSFETs, HEMTs, etc.). For example: in the above-mentioned group III nitride heterojunction, a Two-dimensional electron gas (2 DEG)4, which is an interface of Two materials having different energy bands and lattice constants, generates piezoelectric and spontaneous polarization effects, so that GaN of the buffer layer 3 and the barrier layer 5 interact with each other, and the carrier electron concentration of the conductive pipe is thus increased. In the HEMT structure, the two-dimensional electron gas 4 is spontaneously formed and can be self-sustaining without the need for an external gate bias, referred to as "depletion" mode.
Ohmic contact refers to the contact between metal and semiconductor, and the resistance value of the contact surface is much smaller than that of the semiconductor, so that most of the voltage drops in the Active area (Active region) but not in the contact surface when the device is operated. For example: in the above group III nitride heterojunction, the ohmic contact source and drain metals 7: ohmic contacts to group III nitrides typically require the use of Ti/Al metal compounds. Ohmic contacts, including the present application, are often formed using metal stacks including Ti/Al/X/Au metal stacks (e.g., conventional metal film deposition methods such as e-beam evaporation, sputtering, etc.) may be used. Wherein X can be any one of Ni, Ti, Mo or Pt elements. In addition, the ohmic contact can also not contain gold elements so as to avoid gold pollution in the process. "gold-free" ohmic contacts include Ti/Al/Ti/TiN, Ti/Al/W, Ta/Si/Ti/Al/Ni/Ta, or Ta/Al/Ta. The ohmic contacts are formed by metal deposition and shaping, followed by high temperature annealing techniques.
Insulating layer 8: whether the encapsulation of the ohmic contact layer 7 is reliable depends on the lifetime of the sensor. The function of the insulating layer 8 is to prevent substances in the gas or liquid from contacting each other, which could otherwise short-circuit the current source and drain or affect the accuracy of the sensor. Poor insulation also leads to drift in sensor performance. Possible insulation methods in this application include deposition of insulating metals or other oxides, deposition of high molecular polymers or other organic or inorganic materials.
Sensing region 10: the exposed part (non-insulating) of the barrier layer 5 is between the source and drain electrodes. This area is in direct contact with the test substance. In the simplest case, the sensor region 10 can be an unprocessed surface region of the barrier layer 5 or the cover layer 6. The interaction of the analytes causes a change in the charge density at the sensing surface, resulting in a difference in current density in the channel.
Wherein, the multi-element III nitride in the barrier layer 5 comprises any one of GaN, InN, AlN, AlGaN, InGaN and AlInGaN. When AlGaN is adopted, the thickness of the barrier layer 5 is 15-35 nm, and the molar ratio of Al element is 15-35%; when AlN is used, the thickness of the barrier layer 5 is 2 to 8 nm, which is thinner than when AlGaN is used.
Therefore, the barrier layer 5 can be arranged to optimize the sensing region 10, so that the lower limit of the detection range can be reduced, and the detection of trace substances is facilitated. The vertical distance between the sensing region 10 and the two-dimensional electron gas 4 affects the sensitivity range of the sensor, and in short, the smaller the distance, the smaller the minimum substance content which can be detected by the sensor, i.e. the lower limit of the detection range is low. This will facilitate the detection of very small amounts of chemical components. For example: the response time, the detection range and the sensitivity of the sensor are improved in a manner of sunken etching of the sensing area or thinning of the sensing layer.
In one example, the thickness of the barrier layer 5 is minimized during epitaxial growth, and referring to fig. 2, the thickness of the barrier layer 5 is smaller than that of a conventional HEMT sensor. However, this method is not universal, for example, for the GaN barrier layer 5, in order to ensure the stability of the epitaxial structure, the thickness of the barrier layer 5 cannot be infinitely reduced; if AlN is used as the barrier layer, the thickness may be much smaller than GaN, as previously described.
In one example, another approach is to artificially reduce the thickness of the exposed region of the gate of the sensor during the sensor manufacturing stage on the premise of keeping the thickness of the barrier layer 5 in the epitaxial structure constant, and form a "recessed gate" structure by using an etching technique, which also serves to shorten the distance between the detected object (e.g., the detected object located in the sensing region 10) and the two-dimensional electron gas 4, as shown in fig. 3.
For example: barrier layer 5, including but not limited to group III nitride materials and alloys thereof. The material may be: binary alloy GaN, InN, AlN, ternary alloy AlGaN, InGaN, or even quaternary alloy AlInGaN. In some structures ZnO material may also be used as barrier layer 5. The barrier layer 5 may be doped or intrinsic materials may be used.
The thickness of the barrier layer 5 is not limited to the values given in this example, and depends on the properties of the specific material.
The insulating layer 8 includes any one of insulating metal, insulating oxide, and high molecular polymer.
Preferably, the group III nitride heterojunction, further comprises: a capping layer 6 overlying the barrier layer 5, the composition of the capping layer 6 being doped or using intrinsic materials to interact with the barrier layer 5 to form ohmic contact source and drain metals 7 on the capping layer 6; the exposed covering layer between the ohmic contact source electrode and the drain electrode metal 7 is a sensing area 10; and the insulating layer 8 is also coated on the periphery of the covering layer 6.
For example: the capping layer 6 is located on the barrier layer 5 and, optionally, may be doped or may use intrinsic materials. By providing the capping layer 6, the flatness of the sensor surface may be improved and the ohmic contact (e.g., ohmic contact to the source and drain metals 7) resistance may be reduced.
Wherein the thickness of the covering layer is 1-3 microns.
The sensor can be prepared by the following preparation method of the gallium nitride sensor, and the subsequent relevant description can be referred to, and is not repeated herein.
Through a large number of tests, the technical scheme of the embodiment is adopted, the required gallium nitride sensor is formed by a transistor with a GaN-based HEMT structure by adopting the III-group nitride (such as gallium nitride) semiconductor gallium nitride sensor on a heterogeneous semiconductor substrate (such as an extrinsic semiconductor substrate 2), the detection sensitivity is favorably improved, the sensor miniaturization is realized, and the application field and the potential of the sensor are expanded.
There is also provided, in accordance with an embodiment of the present invention, a multi-sensor system corresponding to a gallium nitride sensor. Referring to fig. 4, a schematic diagram of an embodiment of the system of the present invention is shown. The system comprises:
at least two sensors and a main control circuit; the at least two sensors are connected between the main control circuit and the object to be detected in parallel; and the output signal of the sensor is controlled and analyzed through a main control circuit, so that the concentration detection of the object to be detected is realized.
For example: one of the sensors 1 may comprise an extrinsic semiconductor substrate 2 and a buffer layer 3. The buffer layer 3 is composed of GaN and serves as a current path. One layer on GaN is a barrier layer 5 containing AlGaN. The interaction of GaN and AlGaN results in a two-dimensional electron gas 4 at the interface of GaN. The barrier layer 5 is further covered with a thin cap layer 6 (e.g., comprising GaN) to form ohmic contacts to the source and drain metals 7 with the cap layer 6. An insulating layer 8 is provided outside the layers. The sensing region 10 is exposed to sufficient contact with the surrounding gas, liquid or other medium. To perform a specific analysis, it is necessary to coat the surface of the sensing region 10 with a specific functionalized membrane 11, such as a noble metal, a polymer coating, etc.
At least one of the sensors may be prepared by the following preparation method of the gallium nitride sensor, which is described in the following description and is not repeated herein.
Therefore, through the adjustment of the sensor structure, a series of sensors with different detection ranges are formed, the sensors are combined into a sensor system, and the sensors are arranged in parallel (for example, in parallel) to play a role in the system. Through the use of a plurality of sensors, the detectable range of the system is expanded, and the overall detection precision of the system is improved.
Since the processing and functions implemented by the system of the present embodiment substantially correspond to the embodiments, principles and examples of the sensor shown in fig. 1 to 5, the description of the present embodiment is not detailed, and reference may be made to the related descriptions in the foregoing embodiments, which are not repeated herein.
Through a large number of tests, the technical scheme of the embodiment can solve the problem that the upper limit of the detection range of the sensor is reduced to a certain extent due to the optimization of the sensor, namely, the whole detection range moves towards the micro direction. Thus, for many applications, the upper limit of the detection range is not of concern and therefore does not pose a problem; for certain applications where both the upper and lower limits of the detection range are of interest, the present invention now presents a solution based on the aforementioned sensors.
According to the embodiment of the invention, the preparation method of the gallium nitride sensor corresponding to the gallium nitride sensor is also provided. The method comprises the following steps:
step 1, forming a separated mesa structure on a heterogeneous semiconductor substrate by adopting a plasma etching method; wherein the hetero semiconductor substrate includes: the group III nitride is epitaxially grown on the corresponding extrinsic semiconductor substrate 2.
Wherein the sensor fabrication begins with epitaxial growth of a group III nitride on an extrinsic semiconductor substrate 2. Epitaxial growth techniques are not necessary as the relevant substrates can be customized by third party vendors. A typical epitaxial wafer structure is shown in fig. 5(a), and the epitaxial wafer includes an extrinsic semiconductor substrate 2, a buffer layer, a two-dimensional electron gas 4, a barrier layer 5, and a cap layer 6 (for example, a composition of GaN) stacked in this order from the bottom up.
Wherein the mesa structure may be used for subsequent sensor body portion arrangement, see fig. 5 (b).
And 2, sequentially performing surface oxide removal treatment, metal precipitation and patterning treatment and high-temperature annealing treatment on the basis of the mesa structure, and forming ohmic contact source and drain metal 7 on the top of the mesa structure, as shown in fig. 5 (c).
And 3, sequentially carrying out ohmic contact insulation and metal deposition intercommunication contact treatment and interconnection metal deposition and forming treatment on the basis of a mesa structure with ohmic contact source and drain metal 7 formed on the top, and forming a sensing region 10 between the ohmic contact source and drain metal 7 on the top of the mesa structure.
For example: the ohmic contacts are insulated and leave windows for the outward leads, see fig. 5 (d).
For example: outer lead metal deposition and shaping, see fig. 5 (e).
For example: the outer leads are metal insulated and leave a pad window for connection to an external circuit, see fig. 5 (g).
Preferably, when the sensor uses AlGaN as the barrier layer 5, the sensing region formed by the foregoing process is subjected to a groove etching process to reduce the thickness of the sensing region 10 to a value required for detection.
For example: alternatively, the sensing region 10 (e.g., gate) is recess etched, termed a "recessed gate," see FIG. 5 (f). The recessed gate technique is only applicable to sensors in which AlGaN is used as an isolation layer (e.g., the barrier layer 5), and if AlN is used as the isolation layer (e.g., the barrier layer 5), the AlN can be made thin at the epitaxial stage without performing recessed gate.
And 4, performing functionalization treatment on the sensing region 10 formed by the treatment, and forming a functionalized film 11 on the sensing region.
For example: the functionalized membrane 11 of the sensing region 10 is coated, see fig. 5 (h).
And 5, carrying out metal interconnection insulation or packaging treatment on the mesa structure which is formed based on the ohmic contact source and drain metals 7 and the functionalized film 11 to obtain the sensor 1.
The resulting sensor was prepared by the above procedure, see fig. 6. The sensor includes: mesa 12, insulating layer 8, epitaxial layer 13, substrate 2, and pad 14 for connection to an external circuit.
The sensor prepared by the above steps may also be at least one sensor in the above gallium nitride sensor or multi-sensor system, and for the structure and performance of the prepared sensor, reference may be made to the above description, and details are not repeated here.
Through a large number of tests, the technical scheme of the embodiment can realize the design and manufacture of the III-nitride-based HEMT sensor, improve the structure and improve the sensitivity of the sensor, and has the advantages of simple and reliable operation process, high sensitivity of the obtained sensor, wide detection range and small volume.
It should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
The above description is only an example of the present invention, and is not intended to limit the present invention, and it is obvious to those skilled in the art that various modifications and variations can be made in the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.